1. Field of the Invention
The present invention relates generally to wind turbines, and more specifically to vertical axis wind turbines.
2. Description of the Related Art
Most wind turbine literature pertains to horizontal axis wind turbines, which appear to be the dominant form of wind energy production due to the higher efficiencies of the blades. The high blade efficiency is the result of high tip velocities, however such high velocities result in increased noise and increased damage upon collision with a blade during operation.
Many vertical axis designs have been proposed over the years having lower blade velocities, but they have not achieved widespread adoption in spite of the advantages that come with the lower blade velocities. The main problems have related to structural resonance failures, high manufacturing costs, and the requirement of placement very close to the ground where the wind velocities are lower. Power output is decreased due to the lower velocities near the ground.
Many of the vertical axis structural and cost problems are associated with attempts to recover additional wind energy by adjustments to the blade angle of attack. Other attempts vary the structural shape to accommodate high winds or gusts. Such designs inevitably lead to increased hardware complexity with concomitant increases in failure rates and manufacturing costs.